Battery testing apparatus and method



Oct 1952 s. L. CHRISTIE 2, 3,

BATTERY TESTING APPARATUS AND METHOD Filed March 22, 1948 5 Sheets-Sheet 1 [VI/EN Toe.- SORE/V L'. CHRIS 7/5 Oct. 7, 1952 s. CHRISTIE 2,513,248

BATTERY TESTING APPARATUS AND METHOD Filed March 22, 1948 3 Sheets-Sheet 2 I llllhlxHHl I 504 5 A, CHR/SWE L J%FQ@J Oct. 7, 1952 s. L. CHRISTIE BATTERY TESTING APPARATUS AND METHOD Filed March 22, 1948' 5 Sheets-Sheet 3 By Ms Arne/ways 54mm; MEG/i 525m? df/Axems ELECTROLYTE sPzcmc GRAVITY Patented Oct. 7, 1952 ETHO 8.011511 L. Christie, Los Angeles, Calif., assignor to McColpin-Christie Corp., a corporation of Cali-- fornia Application March 22, 1948, Serial No. 16,258

My invention relates in general to a method of and apparatus for comparing electric quantities of different magnitudes and since the fundamental principles of the invention are particularly applicable to a method of and apparatus for comparing the voltages of the individual cells of a multi-cell battery, such an application will be considered herein for convenience in disclosing the invention.

As is well known in the art,- the condition of a storage battery may be determined by comparing the voltages of the individual cells, the comparison of the cell voltages usually being made with no load on the, battery, while the battery is being charged, and/or while the battery is beingv discharged. If such a comparison of thevoltages oi the cells of an ordinary six-volt storage bat-. tery, for example, discloses that the difference between the maximum and, minimum cell voltages is 0.10 voltor more, a serious defect in the battery is indicated, Adifierence of from 0.10 to 0.15 volt between themaximumand minimum cell voltages of such a battery may,v for example,

indicate a partially short-circuited cell, a broken;

cell, a, crack in the battery case between adjacent cells, ora reduction ,in active plate surface.

other conditions may also produce an excessive able acc racy. lackof; accuracy being the. princi-' pal disadvantage: of the method as heretofore. practiced. Aceordinglmaprimary object of my invention is to provideamethodoi and apparatus for determining, the a difference between he maximum and minimum. cell voltages of a bat ery extremely accurately. r a

As. heretofore practiced, thecell-voltage comparison method ofdetermining the. condition. of:v

a. battery involves measuring the. voltage of each. individual cell. and( then. determining the differ.

once between the maximum. a d. minimum cell voltages by subtraction, the individual cell. voltages conventionally being measured simultanee ously wi h; a plurali yoi: voltmeters. i. Y en. one. for

ea h. cell, or beingmeasured successively with. a. single voltmeter; aiseparate; voltmeter for each cell may producetlargze errors because of;

22 Claims. (01. 175-483) 2 the fact that the usual commercial voltmeter has an error tolerance of i2% of its full scale deflection. Thus, as an example, if three voltmeters, each having a full scale deflection of three volts, are used to measure the individual cell voltages of a six-volt three-cell battery, it will be apparent that the error in the difference between the maximum and minimumv cell voltages may be as much as 10.12 volt. Even if voltmeters of the laboratory type, instead of the commercial type, are used, the error in the difference between the maximum and minimum cell voltages may be as much as 10.06 volt since laboratory type voltmeters ordinarily have an error tolerance of :1% of full scale deflection. In view of the fact that a diiierence of from 0.10 to 0.15 volt between the maximum and minimum cell voltages is indicative of a serious defect in a battery of. the type under consideration, it will be apparent that a possible error of 10.12 volt, or even a possible error of 110.06 volt with a laboratory-type voltmeter, cannot be tolerated.

Even if a single voltmeter is used to measure the individual cell voltages in sequence, it is difficult to obtain the difierence between the maximum and minimum cell voltages with sumcient accuracy due to the fact that errors may be introduced in making and recording the successive readings, in computing the maximum difference, or in connecting the meter to successive cells, irrespective'of whether this is done manually or through. the use of a system of switches. Also, any value obtained for the difference between the maximum and minimumcell voltages when the. battery is being discharged is unreliable if the individual cell voltages. are measured in sequence with. a single meter due to. the factthat the cell'voltages may change between, the time that the voltages of the. first and last cellsv are measured. Since, as herein portant, object. of the present invention is to pro-q vide a method of and apparatus for determining directly witha single. indicator and in asingle operation the difference between the maximum. and Thus, as an example,

minimum cell voltages.

by employing for the indicator a voltmeter for reading only the maximum voltage difference and having a full scale deflection of 0.5 volt while having the usual error tolerance of 12% for voltmeters of the commerical type, it will be apparent that the difference between the maximum and minimum cell voltages may be determined within i0.01 volt. Even greater accuracy may, of course, be obtained by using a voltmeter having a smaller error tolerance, or by using one which has been calibrated to determine its error.

Another object of the present invention is to provide a method of and apparatus for determining the difference between the maximum and minimum cell voltages of a battery which involve establishing an electric quantity proportional to the difference between the maximum and minimum cell voltages and subsequently measuringthis electric quantity in voltage units.

'A further object is to provide a method and apparatus of the character described which involve varying the impedance of an electric circuit in accordance with variations in the difference between the maximum and minimum cell voltages of the battery being tested, and which involve measuring the effect of such an impedance variation in'terms of the difference between the maximum and minimum cell voltages.

Still another object is to provide an apparatus which includes a plurality of saturable reactors 4 voltages of a battery III which is exemplified as a three-cell battery for purposes of illustration, the three cellsbeing identified by the numerals II, I2 and I3, respectively. The battery I may,

for example, be of the type ordinarily used in automobiles.

The apparatus for testing the battery It includes three saturable reactors I5, I6 and I1, there being one such reactor for each of the cells II, I2 and I3 of the battery. Each of the saturable reactors I5, I6 and I! includes two controlling windings which are connected across two of the cells of the battery I0, the controlling windings of the reactor I being identified by the numerals I8 and I9, respectively, those of the reactor I6 being identified by the numerals and 2I,respectively, and those of the reactor I! having their controlling windings connected to the cells of the battery to be tested and having their controlled windings connected to an indicator in such a manner that the indicator is responsive to any difference between the maxi mum and minimum cell voltages.

Another important object of the present invention is to provide a method of compensating for variations in the specific gravity of the electrolyte from one cell to another.

An additional object is to provide apparatus of the characterdescribed which may be used as part of a. control system which is responsive to the condition of a battery connected therein.

Still another object is to provide a method of and apparatus for accurately evaluating the condition of a battery without any necessity for any special skill on the part of the operator.

The foregoing objects and advantages of my invention, together with various others which will be evident hereinafter, may be attained through the utilization of the exemplary embodiments of the invention which are described in detail hereinafter in connection with the accompanying drawings. Referring to the drawings, which are for illustrative purposes only:

Fig. 1 is a diagrammatic view illustrating one embodiment of an apparatus of the invention which is capable of performing the method of the present invention;

Fig. 2 is a diagrammatic view illustrating a second embodiment ofthe invention;

Fig. 3 is a diagrammatic view illustrating a third embodiment of the invention;

Fig. 4is a diagrammatic view illustrating a fourth embodiment of the invention;

Fig. 5 is a diagrammatic view illustrating a fifth embodiment of the invention; and

Fig. 6 is a diagrammatic view illustrating a chart for use in connection with the method of the invention.

Referring particularly to Fig. 1 of the drawings. I show an apparatus for determining the difference between the maximum and minimum @6 being identified by the numerals 22 and 23, respectively. The controlling winding I8 of the saturable reactor I5 is connected across the cell I2 of the battery and the controlling winding I9 thereof is connected across the cell II. Similarly, the controlling-windings 20 and 2I of the saturable reactor IS'are connected across the cells I3 and I2, respectively, of the battery Ill, and the controlling windings 22 and 23 of the saturable reactor I! are connected across the cells II and I3, respectively, of the battery.

The controlling windings of each of the saturable reactors I5, I6 and" are wound in opposite directions with respect to each other and, in the particular construction illustrated, are wound on the center' leg of a three-legged core, the cores of the reactors I5, I6 and I I being identified by the numerals 25, 26 and 21, respectively. Each of the saturable reactors I5, I6 and I! also includes two controlled windings which are connected in series and which are wound in opposite directions with respect to each other on the two outer legs of the corresponding core. The controlled windings of the saturable reactor I5 are identified-by the numerals 3| and are wound in opposite'directions about the outer legs of the core 25, the controlled windings of the reactor I6 are identified by the numerals 32 and are wound in opposite directions about the outer legs of the core 26, and the controlled windings of the reactor I1 are identified by the numerals 33 and are wound in opposite directions about the outer legs of the core 2I. The controlled windings 3I are connected in series, as are the controlled windings 32 and the controlled windings 33.

The pairs of controlled windings 3 I, 32 and 33 are connected in parallel in one arm of a bridge circuit which is indicated generally by the numeral 34, an impedance 35, which is preferably a saturable-reactor as will be discussed in more detail hereinafter, forming the second arm of this "circuit. The third and fourth arms of the bridge circuit 34 are formed by portions 36 and 31 of a secondary winding 38 of a transformer 39, the transformer having a primary winding 40 which is connected to an alternating current source. A suitable indicator. exemplified as a voltmeter 4|, is connected across one diagonal of the bridge circuit 34, one terminal of the voltmeter being connected to the junction between the first and second arms of the bridge and the other-terminal thereof being connected to the junction "of the third and fourth arms of the bridge.'-

Considering the operation of the testing apparatus illustrated in Fig. 1 of the drawings, it will'be apparent that since the controlling windings I8 and I? of the saturable reactor l5 are connected across the cells Hand II, respectively, of the battery I and are oppositely wound, the net flux produced by the controlling windings I8 and I9 will be proportional to anydifference between the voltages of the two cells to which the windings are connected. As is well known in the art, the net flux produced by th controlling windings I8 and I9 of the saturable reactor I increases the flux through one of the outer legs of the core carrying one of the controlled windings 3| and decreases the flux through the other outer leg carrying the other controlled winding. The net result is a decrease in the impedance of the controlled windings 3| of the saturable reactor I5 irrespective of the direction of the netflux produced by the controlling windings I8 and I9, this decreasein impedance being proportional to the net flux and thus being proportional tothe difference between the voltages of the cells II" and I2 of the battery III. The decrease in impedance/of the controlled windings 3| of the ,saturable reactor I5 results in an increase in the current flowing through these windings, such current increase being proportional to the difference between the voltages of the'cells II and I2'of the battery.

The saturable reactor I6 operates in a similar manner with respect to the cells I2 and I3 of the battery I0. In other words, in the event of a diiierence between the voltages of the cells I2 and I3, the impedance of the controlled windings 32 of the reactor I6 is reduced toincrease the current through the controlled windings 32 an amount proportional to the cell voltage difference. Similarly, a difference between -the'volt-' ages of the cells II and I3 of the battery will produce an increase in the current through the controlled windings 33 of the saturable reactor H which is proportional to the difference between the voltages of these cells. 1

Thus, any difference between the voltages of the cells II and I2 of the battery I0 appears as an increase in the current flowing through the controlled windings 3| of the saturable reactor I5, any difference between voltages of the cells I2 and I3 appears as an increase in the current flowing through the controlled windings 32 of the reactor I6, and any difference between the voltages of the cells II and I3 appears as an increase in the current flowing through the con-- trolled windings 33 of the reactor I I, the sum of such increases in the current flowing through the controlled windings 3|, 32 and 33 being proportional to the difference between the maximum and minimum cell voltages of the battery. In order to demonstrate this, it'will be assumed that emax designates the maximum cell voltage, 1. e., the voltage of the cell of the battery-I 0 having the highest voltage, and that 6min designates the minimum cell voltage. The intermediate cell voltage will be designated by Cint. Thus, the current increases in the controlled windings or the saturable reactors I5, I6 and I1 resulting from differences in the voltages of the cells I I, I2 and I3 are proportional to (emax em'ie), (rnaxeint) and (ems-emu), but not necessarily respectively. Consequently, the sum of thecur rent increases is proportional to (e ail- 6min) since ems cancels out when 'ema.x-e 1 (crux-elm) and (emu-elem) are totaled;

Thus, it will be apparent that since the pairs of controlled windings 3|,"32 and 33' are connected in parallel, any increase in the current flowing through the arm of the bridge circuit 34 in which the controlled windings are connected twccnthe voltages of the cells II, I2 and I3 of the battery III will produce a change in them-- dioation of the voltmeter III which bears a direct relation to the difference between the maximum and minimum cell voltages.

The scale of the voltmeter 4| may be so calibrated that the difierence between the maximum and minimum cell voltages may be read directly therefrom, or it may be divided into zones marked "Good, fDg ubtfulfi Bad, or the like, to denote the condition of the battery.

It will thus be apparent that the difference be tween the maximum and minimum cell voltages of the battery I0 may be determined in a single operation with a single indicator so that an accurate evaluation of the differenceresults. As an example, if I employ for the voltmeter an instrument having a. full scale deflection of 1.0 volt and having an error tolerance of i5% of the full scale deflection, the maximum meter error would be $0.05 volt: If the circuit is'so proportioned that a cell voltage diiference.of.0.15 volt provides areadin'g of 0.75 volt on. the meter 4| and a cell voltage difference of 0.16 volt provides a reading of 0.80 volt, then a meter error. of $0.05 volt (5% of full scale'deflection') would be the equivalent of an error in cell voltage difference of only .i0.01'volt. It will be understood that even more accurate results may be obtained by employing a voltmeter having a smaller fullrscale deflection, or by employing avoltmeter having a f smaller error tolerance.

An important feature of the present invention resides in the employment of an'impedance for the impedance 35 in the second arm of the bridge circuit 34 which increases with an increase in the current flowing through it. As is well known in the art, an iron core reactor has this characteristic when used at'a very low flux density. This characteristic can also be obtained at a higher flux density by presaturating the core with a separate field. Accordingly, I prefer to employ for the impedance 35 a saturable reactor having controlled windings which areconnected in series in the second arm of the bridge "circuit 34, and having a controlling winding 45 which is connected to a constant voltage, direct current source. The controlled windings 44 are oppositely wound on the two outer legs of a three-legged core 46 in the particular construction illustrated, and the controlling winding 45 is wound on the inner leg of the core. The function of the controlling windin 45 is to presaturate the core 46 with the result that the sensitivity of the bridge circuit 34 is greatly increased over that which could be obtained by using a fixed impedance, or an impedance which decreases with an increase in the current flowing therethrough, the latter being the case with reactors which are'used at r ormal values of flux density without presaturaion.

In order to prevent damage to the voltmeter 4 I, I prefer to operate the saturable reactor 35 near the reversal point on its reactance-current curve so that, in the event of high degrees of saturation of the reactors I5, I6 and H, a decrease in reactance of the reactor 35 occurs due to an increase in the. current flowing through the controlled windings 44 thereof above the current value for maximum reactance. This eliminates the high degree of unbalance ofthe bridge circuit 34 which would otherwise result from high de grees of saturation of the reactors 15,16 and I1 and thus prevents damage to the voltmeter 4|. Excessive saturation of the reactors I .5, I6 and I1. may, for example; result from very large differences between the cell voltages of the battery I0, or may result from an open connection to one of the cells, the latter having the effect of producing a cell voltage diiference'equal to the waitage of one of the cells. Thus,.by operating the saturable reactor 35'near the reversal point on its reactance-current curve, I obtain high sensitivity in the normal operating range and low sensitivity outside of the normal operating range.

In Fig. 1 of the drawings, 1 have shown the controlling winding 45 of the saturable reactor 35 as being connected to the constant voltage source through a variable resistor 41; The resistance of the resistor 41 may be varied to compensate for variations in ambient temperature and the like.

As previously mentioned, evaluating the condition of a battery by the cell-voltage comparison method preferably includes determining the difference between the maximum and minimum cell voltages with no load on the battery, while the battery is being charged, and while the battery is being discharged. Referring to Fig. 1 of the'drawings, in order to permit determination of the difierence between the maximum and minimum cell voltages while the battery I is being charged, it may be connected to a suitable direct current source by leads 50 and the battery being connected to the source through a switch arm 52 which may be moved into engagement with a contact 53 to complete the circuit between the battery and the source of charging current. A

resistor 54 is connected to the lead and may be connected in serie with the battery It! by moving the switch arm 52 into engagement with a contact 55 at one end of the resistor to permit testing the battery It! while it is being discharged. Any desired value of resistance may be employed for the resistor 54, depending upon the rate of discharge desired.

In Fig. 2 of the drawings, I show an embodiment of the present invention which differs from that shown in Fig. 1 in that the number of saturable reactors directly associated with the battery being tested is equal to the number of battery cells minus one, rather than being exactly equal to the number of battery cells. In Fig. 2, I show a battery 60, exemplified as a three-cell battery having cells BI, 62 and 53, across which is connected a resistor 64, the latter being divided into as many equal parts as there are cells in the battery. Thus, when a three-cell battery such as the battery is to be tested, the resistor (N is divided into three equal parts 65, 66 and 6? corresponding to the cells GI, 62 and 63, respectively.

The embodiment shown in Fig. '2 of the drawings includes two saturable reactors H and 12 having controlling windings l3 and I4, respectively, and havin pairs of controlled windings l5 and 16, respectively. The controlling winding 13 of the saturable reactor II is connected to the dividing point I1 between the parts 65 and 66 nected in series with each other, the same being true of the controlled windings it of the reactor 12. The pairs of controlled windings l5 and 16 of the saturable reactors H and 12 are connected in parallel in one arm of a bridge circuit 80 having in its second arm a third saturable reactor 8| which serves the same purpose as the saturable reactor 35 in the embodiment illustrated in Fig. 1 of the drawings, the reactor 8| including controlled windings 82 connected in series, and including a controlling winding 83 which is connected to a constant voltage, direct current source through a variable resistor 84. The third and fourth arms of the bridge circuit 80 are formed by two parts 85 and 86 of a resistor 81, a secondary winding 88 of a transformer 89 having a primary winding 90 connected to an alternating current source being connected across the resistor 81. A suitable indicating device, exemplified as a voltmeter 9|, is connected across one diagonal of the bridge circuit 80, one terminal of the voltmeter being connected to the junction between the first and second arms of the bridge and the other terminal thereof being connected through a movable contact 92 to the junctio between the third and fourth arms of the bridge. The purpose of the movable contact 92 is to permit varying the relative resistances of the third and fourth arms of the bridge circuit 80 to permit balancing the circuit and, if desired, this construction may be incorporated in the embodiment illustrated in Fig. l of the drawings.

In order to permit testing the battery 60 while it is being charged, I provide leads 95 and 96 for connecting the battery to a suitable source of direct current, a switch arm 9'! interposed between the battery and the direct current source being movable into engagement with a contact 98 to complete the circuit between the battery and the source of charging current. In order to permit testing the battery 60 While it is being discharged, I provide a resistor 99 which is connected to the lead 95 and which may be connected across the battery 90 by moving the switch arm 91 into engagement with a contact I00 thereon. Thus, with the switch arm 91 in the position shown in Fig. 2, the battery 60 may be tested under no load, or may be tested while being charged or discharged by moving the switch arm 91 into engagement with the contact 98 or the contact I09, respectively.

Considering the operation of the embodiment of my invention which is illustrated in Fig. 2 of the drawings, it will be apparent that if the voltages'of the cells 6|, 62 and 63 of the battery 60 are equal, the dividin points 11 and 18 between the parts of the resistor (it and the junctions between the cells of the battery will all be at the same potential so that no current will flow through the controlling windings 73 and 14 of the saturable reactors H and 12. However, if the voltage of one of the cells of the battery 60 deviates from 1/11. of the total battery voltage, where n represents the number of cells (in this case 3), current will flow i at least one of the controlling windings 13 or 14 of the saturable reactors H or 12, thereby decreasing the impedance of the corresponding controlled windings 75 or 16 and permitting an increase in the current flowing therethrough. The total increase in current through the controlled windings 15 and 16 is a function of the difierence between the maximum and minimum voltages of the cells of the battery 69, and, since the pairs of controlled windings l5 and 16 are connectedv in parallel, the voltmeter I9 91 will respond to the difference between the maximum and minimum zce'll voltages. ns {previously indicated in connection with the embodiment illustrated in Fig. 1,:the scale of the voltmeter 9I may be .so calibrated that the adifi'erence betwee the maxinm'mrandiminimumicell voltages may be read directlytherefrommr may bediv-i-ded into zones, etc. p

In Fig. 3 of the sdrawingslshow an embodiment of my invention which, impart, ris:identica1 to that shown in.1Fig.- 2, 'thatlrnortion'of the circuit shown in Fig. 3 whichiies withinithe brokenlines Illl being identical to ifl'lfl'tEDOBfiOIl of the circuit 'of Fig. 2 whichlies withinithe broken lines EH12.

The components of the embodiment illustrated ,2

in Fig.3 which .lie within the broken-lines I identified by the numerals used to identify he corresponding components of the embodiment illustrated in -Eig. '2 which Jlie within the broken lines I02.

The apparatus i-llustrated;-'in; E'ig..-3 '0'! the'drawings includes apair 10f saturable reactors H I and H2 having controlling windings H3 and Il?4,.respectively, the winding I I-3 being-connected to the dividing point H beiwveenathe .parts 55 and =66 of the resistor and to the junction between the cells ii I and 6-2 :of the battery :60. :and the winding IIA being connected :to the dividing jpoint I8 between the parts 66 and =6! *lOf :this resistor and to thejunction betweenthecells w :and 63 of the battery. :Eachof the .zsaturable reactors vIII and H2 includes two controlled windings same purpose as the .saturableueactcrs 335 and'BI of the embodiment shown-in Figs. 11 :a-nd 210i lth drawings, respectively.

Connected across one @dia'gonal 01? the bridge circuit -I I9 is a secondary winding 1123 :of re. transformer I24, the latter having another secondary Winding I .and .a prirnary winding I26. The 1 grids of a duo-triode tube 129 are ;;connected across the other diagonal of the rbridge --circuit, this tube havin two Tgrids |3 4Une1fiWhiChiS connected through :8. resistor fi-I 3:I to thegijun'ction between'the controlled windings III Sranwtheiimpedance I2 I ,and the other of ,whichxisconnected through another resistor 'I:3.I toitheijuncti'on between the :controlledwindings H6 and the zimpedance I22, Theitub'el29fis pmvidedtwith-two plates I32 which are :connectedthrough .loadzresistors I33 to one terminal :of aniindicatingvdevice, exemplified as fa" voltmeter I3'4. The foth'er terminal of the yoltmeteriis connected :to one end of th secondary winding I25, the otherend of the secondary Winding:being connected to' the junction between the impedances' n l and I'22-"o'f the bridge circuit M9. "The tube I29" -is 1')rovibled with cathodes I35 whicheare 'connectedito ah intermediate point on the secondary winding I525 of the transformer I24. Although the-plates "I 32 are shown as connected to an alternating current source, they may 'be connected to -ia dii' ect current source if desired. v

It will be apparent that the mite I 29 eser vesato arrears of the controlled windings .I.I:.5 ,and .I I5 oi the saturablereactors III :and :I I2 due-to differences between the voltages of'th'e :cells '51, 62 and 53-.0f the battery 56.0 so :as .to increase .:the deflection iof .the voltmeter 13-14 for a given differencebetween the maximum and minimum-cell voltages thereby increasing the sensitivity ofsthe .zapparatus. vAlthough .I have shown .in. Fig. :3 :ofathe drawings a modification aof the embodiment :s-howln ainil lig. 2, it *be understood that the embodiment illustrated .in Fig; 1 mayibe modi- -fied in a similar manner :if greater sensitivity is desired. l

The embodiment-ofimylinuentionwhichjiszillusftrate'cl in fig. 4 of the drawingais, intpart, :identical ito that illustrated in $1,;th91t portion :o'f the circuit shown in Fig. A which lies within the broken flil'iS =Mi| vbeing. identical to that wportion :of'the-circuitnf Fig. :1 which-lies within .thebroksen :lirres M12. CDh'oseacomponen'ts. of the embodiment illustrated :in Fig. 4which :-lie within :the broken lines I541 are identified by .the inumerals used to identify the corresponding.icomponerits of the :embodiment illustrated in 11 which lie :within theibrokentlines I142.

The:apparatusillustrated in Fig. 40f the drawiingsincludesithree saturablezreactorsil 45, :MB and it which correspond. to the saturable reactors 1L5, I6 :and aIiI, respectively, .of :the embodiment illustrated injFig. .=l. The;saturable .reactorMB :is 'aprovided with controlling windings chill. and 'flflfl'which correspond .to Zthe controlling windings t8 :and '19 :of ithe :saturabl'e reactor 15 land which are connected'tothelbattery I0 inithie same mannor, the saturable reactor I46 .is provided. with .contrcilling windings I50 and :I;5.I which :cor'rezspond to ithe 'controlling'windings 20 and 32 I .ofe'the .saturable reactor ..I:6 and 'which are..connect'ed to the battery Illintheisame manneryand dzheisaiturable reactor A141 .is .pllOVidGd with controlling windings 452 and J53 which correspond .to the controlling windings 122 and 23 of the saturable rea'ctor 5'11 and :which :are also connected to 'the abatteryiinxtheisame manner. The @reactors 1135, I45 :and .MI ar respectively :provided with pairs 'oi-zcontrolle'd windings I55, IL56zand:I5.'I whichtcorirespond'itottheicontrolled windings 31, 32-, and 33 thezizeactorsitfi, IIGandiIJ- 1 a .ilinstead 0f being connected :in parallel in one [arm zof i-a ibridge circuit as in the :embodiment lillustratedfiniEig. 1 of :theldrawings, theipair of controlled windings 455, I56 and I5! 10f .the relactors M5,- llllfi and IMF! are connected iniseparate bridge. circuits lisil I-'62,and I163, respectivelyseach pair of controlled windingsxlz55, I=56.and I5:l:forming [one a arm of the corresponding bridge :circuit. Adj acentarms :of rthe bridge. circuits I16 I I 62.. and :1163 :comprise impedances 464, I65 and .l-66.::respectivelyl *Preferably, the .impedances 4:64, .165 and are :formed by the controlled .windings =o'frsaturableireactors L(the:controlled windings :of which PEIB rnotsshown) which perform functions csimila'r to'ithat performed 'by:th'e saturable ire- :actor 1350f the embodiment illustrated in Fig. .1 of 'the drawings. The third "and .lfourth :arms rof the ib'ridge icircuitsllil, IIS62 and0I63 .are formed ibyqsecondary windings .1161, 158 and I69, .rspectivel-y, :of a transformer, such secondary wind ings being inductively coupled with a .primary "winding flll zwhich may be connected to;a suitable alternating:current source. r r I "The :bridge circuits I It I H362 :and I63 :are soonnectetliinsserie's"in-ithe:manner illustratedliniFig. :ofithe drawings ito zforn'irazcl'osed circuit a :voltamplify the effect of reductions initheiiinirecanoes its l being ECtedii-n ithaeirciiit. :Enet- I62 and. I 63 for. balancing purposes. apparent that ifany difierences between the cell erably, a potentiometer. I12 is connected in series with :the voltmeter "land bridge. circuits .I6I, It will be voltagesoi the battery 10 obtain, the impedances of the'controlled windings I55, I56. and II of to that shown in Fig. 2, that portion of the circuit-shown in Fig. 5 which lies within the broken lines I80 being identical to that portion of the circuit of Fig. 2 which lies within the broken lines I02. The components of the embodiment illustrated in Fig. 5 which lie within the broken lines I80 are identified by the numerals used to identify the corresponding .components of the embodiment illustrated in Fig. 2 which lie within the brokenlines I02.

' The apparatus illustrated inFig. 5 of the drawings includes a pair of saturable reactors I8I and I82 having. controlling windings I83 and I84 which correspond to the controlling windings I3 and I4, respectively, of the saturable reactors II and I2 of the embodiment illustrated in Fig. 2 of the drawings, the controlling windings I83 and I84 being connected to the battery 60 in the same manner as the controlling windings I3 and I4. The saturable reactors I8I and I82 are also provided with pairs of controlled windings I85 and I86, respectively.

Instead of connecting the controlled windings I85-and I86 of the saturable reactors I8I and I82 in parallel through av commonimpedance as is the case with the controlled windings I3 and 14 of the saturable reactors II and I2 of the embodiment illustrated in Fig. 2 of th drawings, I connect the controlled windings I85 and I86 across an alternating current source, exemplified as .a secondary winding I8! of a transformer I88 which includes a primary winding I89, through separate impedances I90 and I9I, respectively. It will be noted that the controlled windings I85 and I86 of the saturable reactors I8I and I82 are connected to opposite sides of the alternating current source. Preferably, the impedances I90 and I9I are formed by the controlled windings of saturable reactors which perform functions similar to that of the controlled windings 82 of the saturable reactor 8I ofthe embodiment illustrated in Fig. 2 of the drawings.

. A voltmeter I92 is connected between the junc- :tionof the controlled windings I85 and the impedance I90 andthe junction of the controlled windings I86 and the impedanc I9I, the voltmeter thusv being connected across one diagonal of a bridge circuit'formed by the controlled windings I85 and I86 and the impedances I90 and I9I. It will be apparent that if difierencesin the cell voltages of the battery 60 obtain, such differences will produce a deflection of the voltmeter I92, the voltmeter deflection, as in the previously discussed embodiments, bearing a direct relation to the maximum cell voltage difference.

Although I have described the operation of the foregoing embodiments of my invention as used to obtain actual measurements of the difierences between the maximum and minimum, cell voltages with the voltmeters 4|, 9|, I34, Ill and I92,

these embodiments may be used to control the .7

operation of other apparatus in response to a difference between the maximum and minimum values of various electric quantities, e. g., the difierence between the maximum and minimum cell voltages of abattery. In the embodiment illustrated in Fig. lot the drawings, for example, the reduction in-impedance of the controlled windings 3I, 32 and 33 of the saturable reactors I5, I6 and Il resulting from differences in the voltages of thecells II, I2 and I3 of the'battery I0 may be utilized to actuate a warning or control device (not-shown) instead of the voltmeter 4 I, such a warning or control device being substituted for the voltmeter in th bridge circuit 34 andproviding either a visible or an audible signal or a control potential when the difference between the maximum and minimum cell voltages reaches a predetermined value. Similarly, devices of various other types may be substituted for the voltmeter 4| in the embodiment illustrated in Fig. 1 of the drawings, or for the voltmeters in the embodiments illustrated in Figs. 2 to 5.

As hereinbefore' discussed, one of the features of the present invention resides in the provision of a method of compensating for variations in the specific gravity of the electrolyte from one cell to another when the condition of the battery is being determined by the cell voltage comparison method. As will be apparent to those skilled in the-art, if thespecific gravity of the electrolyte in one cell of a battery differs from that in another cell, a difference between the voltages of such cells may exist even if the battery is otherwise in good condition. For example, such a difference between the specific gravities of the electrolyte in the two cells would result if, through careless servicing or otherwise, acid is removed from one of the cells and placed into the other. Although it is necessary to transfer a large amount of acid from one cell to another to cause a difference of, for example, 0.10 volt or more between the voltages of the two cells in a fully charged battery, I prefer to compensate for specific gravity differences in order to permit accurate evaluation of any difference between the maximum and'minimum cell voltages due to factors other than specific gravity inequalities.

I have found that the desired result may be attained by determining the difference between the maximum and minimum cell voltages when the specific gravityof'the electrolyte is at a value such that its resistivity is a minimum. Referring to'Fig. 6 of the drawings, I show, for

purposes'of illustration, a graph which indicates the variations of the resistivity of sulphuric acid with specific gravity for different temperatures, the resistivity versus specific gravity curve for each temperature having a point thereon where the resistivity is a minimum. It will be apparent'that at the point where the gradient of each specific gravity versus resistivity curve is zero, 1. e., at the point on each specific gravity versus resistivity curve where the value of the specific gravity of the electrolyte is such that its resistivity is a minimum, relatively large variationsin specific gravity of the electrolyte will not change the resistivity thereof appreciably. For example, considering the lowermost curve in the graph in Fig. 6, i. e., the curve for an electrolyte temperature of 30 C., it will beseen that the specific gravity may be varied throughout the range of from 1.200 to 1.250, for example. without changing the resistivity appreciably. v

termined by the maximum difference between the voltage Ofthe battery cells; and applying said single electric value to said instrumentality.

9. In an apparatus responsive to any difference between the maximum and minimum cell voltages of a battery having at least three series-connected cells, the combination of: a number of series-connected resistors equal to the number of battery cells; means for connecting said seriesconnected resistors in series with the battery; a

number of controlling winding means equal to the number of resistors and battery cells minus one; means for connecting one side of one of said controlling winding means 1 between a pair of the battery cells and for connecting the other side thereof between a pair of said resistors; means for connecting one side of another of said controlling winding means between another pair of the battery cellsv and for. connecting the other side thereof between another pair of said resistors; a number of controlled winding means equal to the number of controlling winding means, said controlled winding means being magnetically coupled with said controlling winding means, respectively, whereby anyelectric current flowing through said controlling winding means due to difierences between the voltages of the battery cells produce in said controlled winding means electric quantities respectively determined by said electric currents; and electric circuit means for combining said electric quantities into a single electric value determined by any difference between the maximum and minimum battery cell voltages.

10. An apparatus as set forth in claim 9 wherein said electric circuit means comprises a bridge circuit having said controlled winding means therein, said apparatus additionally including an instrumentality responsive to said single electric value connected across said bridge circuit.

11. An apparatus as set forth in claim 10 wherein said controlled winding means are connected in parallel in one arm of said bridge circuit.

' 12. In an apparatus responsive to any difference between the maximum and minimum cell voltages of a battery having at least three seriesconnected cells, the combination of: a number of controlling winding means equal to the number of battery cells, each of said controlling winding means including a pair of opposed controlling windings; means for respectively connecting said controlling windings of one of said controlling winding means across the battery cells of one pair of such cells; means for respectively connecting said controlling windings of another of said controlling winding means across the battery cells of another pair of such cells; means for respectively connecting said controlling windings of still another of said controlling winding means across the battery cells of still another pair of such cells; a number of controlled winding means equal to the number of controlling winding means, said controlled winding means being magnetically coupled with said controlling winding means, respectively, whereby any electric currents in said controlling winding means due to differences between the voltages of the battery cells induce in said controlled winding means impedance variations respectively determined by said electric currents; and electric circuit means connected to all of said controlled winding means for combining 'said impedance variations into a single electric CPI connected to all of said controlled winding means value determined by the maximum difference between the voltages of thebattery cells. I

13. An apparatus as set forth in claim 12 wherein said electric circuit means comprises a bridge circuit means having said controlled winding means therein, said apparatus additionallyincluding an instrumentality responsive to said single electric value connected across said bridge circuit means.

14. An apparatus as set forth in claim 13 wherein said controlled winding means are connected in parallel in one arm of said bridge circuit means.

15. In an apparatus for testing a battery having at least threecells with a single meter responsive to the maximum difierence between the voltages of the battery cells, the combination of: a number of saturable reactors at least equal to the number of battery cells minus one, each of said saturable reactors having a controlling winding means and a controlled winding means magnetically coupled therewith; electrical circuit means connected to all of said controlling Winding means and connectible to the battery cells for producing in said controlling winding means controlling electric quantities representative of voltage differences between the battery cells, whereby to establish in said controlled winding means controlled electric quantities respectively determined by said controlling electric quantities; and electrical circuit means connected to all of said controlled winding means and to said meter for combining said controlled electric quantities into a single electric variable applied to said meter and representative of the maximum difference between the voltages of the battery cells.

16. An apparatus according to claim 15 wherein the electrical circuit means last defined includes a bridge circuit, and wherein all of said controlledwinding means are connected in parallel in one arm of said bridge circuit, said meter being connected across said bridge circuit.

17. An apparatus according to claim 15 wherein the electrical circuit means last defined includes a bridge circuit, and wherein said controlled winding means are disposed in different arms of said bridge circuit, said meter being con- :nected across said bridge circuit.

cludes a bridge circuit means in which said controlled winding means are connected, said apparatus further including another saturable reactor in said bridge circuit means, and further including means for presaturating the core of said other saturable reactor.

20. In an apparatus for determining the maximum difference between the values of electric characteristics of a plurality of electrical elements, the combination of: a number of controlling winding means at least equal to the number of said electrical elements minus one; electrical circuit means, including electrical conductors connected to said controlling winding means and connectible tov said electrical elements, for connecting said controlling winding means to different ones of said electrical elements so as to establish in said controlling winding means controlling electric quantities representative of differences between the valves of said electric char acteristics; a number of controlled winding means equal to the number of controlling winding means, said controlling winding means being coupled with said controlled winding means, respectively, so as to establish in said controlled winding means controlled electric quantities respectively determined by said controlling electric quantities; a meter responsive to the maximum difference between the values of said electric characteristics; and electrical circuit means connected to all of said controlled winding means and to said meter for combining said controlled electric quantities into a single electric variable applied to said meter and representative of the maximum difierence between the values of said electric characteristics.

21. An apparatus according to claim 20 wherein the number of controlling winding means is equal to the number of said electrical elements minus one, wherein said electrical elements are connected in series, and wherein the first electrical circuit meansdefined inclaim 20 includes:

a number of series-connectedresistors equal to the number of said electrical elements; electrical conductors for connecting said series-connected resistors in series with said series-connected electrical elements; and conductors for connecting one side of each of said controlling winding means between a pair of said electrical elements and for connecting the other side thereof between a pair of said resistors.

22. An apparatus as defined in claim 20 wherein the number of controlling winding means is equal to the number ofsaid electrical elements,

wherein each of said controlling winding means includes a pair of controlling windings, and

wherein the first electrical circuit means defined in claim 20 includes conductors for connecting said controlling windings across said electrical elements, the controlling windings of each controlling winding means being connected across different electrical elements.

SOREN L. CHRISTIE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

